U.S. patent number 11,170,714 [Application Number 17/001,737] was granted by the patent office on 2021-11-09 for pixel circuit, method for driving the same, display panel and display device.
This patent grant is currently assigned to BOE Technology Group Co., Ltd., Chengdu BOE Optoelectronics Technology Co., Ltd.. The grantee listed for this patent is BOE Technology Group Co., Ltd., Chengdu BOE Optoelectronics Technology Co., Ltd.. Invention is credited to Sheng Hu, Ziyang Yu.
United States Patent |
11,170,714 |
Hu , et al. |
November 9, 2021 |
Pixel circuit, method for driving the same, display panel and
display device
Abstract
The present disclosure discloses a pixel circuit, a method for
driving the same, a display panel and a display device. The pixel
circuit includes: a first switching transistor, a second switching
transistor, a first capacitor, a second capacitor, a driving
transistor, and a light emitting device; where a gate electrode of
the first switching transistor is connected with a scanning signal
end, a first electrode of the first switching transistor is
connected with a reference signal end, and a second electrode of
the first switching transistor is connected with a gate electrode
of the driving transistor; and a gate electrode of the second
switching transistor is connected with a light emitting control
signal end, a first electrode of the second switching transistor is
connected with a first power supply end, and a second electrode of
the second switching transistor is connected with a first electrode
of the driving transistor.
Inventors: |
Hu; Sheng (Beijing,
CN), Yu; Ziyang (Beijing, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
Chengdu BOE Optoelectronics Technology Co., Ltd.
BOE Technology Group Co., Ltd. |
Chengdu
Beijing |
N/A
N/A |
CN
CN |
|
|
Assignee: |
Chengdu BOE Optoelectronics
Technology Co., Ltd. (Chengdu, CN)
BOE Technology Group Co., Ltd. (Beijing, CN)
|
Family
ID: |
1000005918861 |
Appl.
No.: |
17/001,737 |
Filed: |
August 25, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20210074211 A1 |
Mar 11, 2021 |
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Foreign Application Priority Data
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Sep 5, 2019 [CN] |
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201910836923.3 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G
3/3233 (20130101); G09G 2300/0426 (20130101); G09G
2320/0233 (20130101) |
Current International
Class: |
G09G
3/3233 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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104409042 |
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Mar 2015 |
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CN |
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106920508 |
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Jul 2017 |
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CN |
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108364610 |
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Aug 2018 |
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CN |
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Other References
Office Action for corresponding Chinese Application 201910836923.3
dated Jun. 24, 2020. cited by applicant .
Office Action for corresponding Chinese Application 201910836923.3
dated Sep. 22, 2020. cited by applicant .
Decision of Rejection for corresponding Chinese Application
201910836923.3 dated Dec. 22, 2020. cited by applicant.
|
Primary Examiner: Khoo; Stacy
Attorney, Agent or Firm: Arent Fox LLP Fainberg; Michael
Claims
What is claimed is:
1. A pixel circuit, comprising: a first switching transistor, a
second switching transistor, a first capacitor, a second capacitor,
a driving transistor, and a light emitting device; wherein a gate
electrode of the first switching transistor is directly connected
with a scanning signal end, a first electrode of the first
switching transistor is directly connected with a reference signal
end, and a second electrode of the first switching transistor is
directly connected with a gate electrode of the driving transistor;
a gate electrode of the second switching transistor is directly
connected with a light emitting control signal end, a first
electrode of the second switching transistor is directly connected
with a first power supply end, and a second electrode of the second
switching transistor is directly connected with a first electrode
of the driving transistor; a first end of the first capacitor is
directly connected with a data signal end, and a second end of the
first capacitor is directly connected with a second electrode of
the driving transistor; a first end of the second capacitor is
directly connected with the gate electrode of the driving
transistor, and a second end of the second capacitor is directly
connected with the second electrode of the driving transistor; and
an anode of the light emitting device is directly connected with
the second electrode of the driving transistor, and a cathode of
the light emitting device is directly connected with a second power
supply end.
2. The pixel circuit according to claim 1, wherein a capacitance
value of the second capacitor is greater than that of the first
capacitor.
3. The pixel circuit according to claim 1, wherein each of the
first switching transistor, the second switching transistor and the
driving transistor is an N-type transistor.
4. A display panel, comprising the pixel circuit according to claim
1.
5. A display device, comprising the display panel according to
claim 4.
6. A method for driving the pixel circuit according to claim 1,
comprising: in a compensation phase: turning on the first switching
transistor by the scanning signal end, and loading a low-potential
signal to the gate electrode of the driving transistor by the
reference signal end; and turning on the second switching
transistor by the light emitting control signal end, and loading a
high-potential signal to the first electrode of the driving
transistor by the first power supply end; in a data writing phase:
turning on the first switching transistor by the scanning signal
end, and loading a high-potential signal to the gate electrode of
the driving transistor by the reference signal end; turning off the
second switching transistor by the light emitting control signal
end; and loading a data signal to the second electrode of the
driving transistor by the data signal end; and in a light emitting
phase: turning off the first switching transistor by the scanning
signal end; and turning on the second switching transistor by the
light emitting control signal end, and loading the high-potential
signal to the first electrode of the driving transistor by the
first power supply end, for controlling the driving transistor to
drive the light emitting device to emit light.
7. The method according to claim 6, wherein in the data writing
phase, time of turning off the first switching transistor by the
scanning signal end is earlier than that of stopping loading the
data signal by the data signal end.
8. The method according to claim 6, wherein in the data writing
phase, time of stopping loading the high-potential signal by the
reference signal end is later than that of turning off the first
switching transistor by the scanning signal end.
9. The method according to claim 6, wherein in the data writing
phase, time of stopping loading the high-potential signal by the
reference signal end is later than that of stopping loading the
data signal by the data signal end.
10. The method according to claim 6, wherein before the
compensation phase, the method further comprises: in an
initialization phase: turning on the first switching transistor by
the scanning signal end, and loading the low-potential signal to
the gate electrode of the driving transistor by the reference
signal end; and turning on the second switching transistor by the
light emitting control signal end, and loading the low-potential
signal to the first electrode of the driving transistor by the
first power supply end.
Description
The present disclosure claims the priority from Chinese Patent
Application No. 201910836923.3, filed with the Chinese Patent
Office on Sep. 5, 2019, and entitled "PIXEL CIRCUIT, METHOD FOR
DRIVING THE SAME, DISPLAY PANEL AND DISPLAY DEVICE", which is
hereby incorporated by reference in its entirety.
FIELD
The present disclosure relates to the technical field of display,
and in particular to a pixel circuit, a method for driving the
same, a display panel and a display device.
BACKGROUND
An organic light emitting diode (OLED) is one of hotspots in the
field of research of flat panel displays nowadays, and compared
with a liquid crystal display (LCD), an OLED display has the
advantages such as low energy consumption, low production cost,
self-illumination, wide viewing angle and high response speed. At
present, the OLED display has begun to replace a traditional LCD
display in the field of displays such as a mobile phone, a tablet
personal computer and a digital camera.
With the development of economy, customers have put forward a
higher requirement for the quality of an electronic product, while
there is also a higher expectation for a display screen serving as
a human-computer interaction window. In order to achieve better
visual experience, a frame displayed by a display is required to be
delicate enough, which requires that the resolution ratio of the
display screen reaches a higher level, while the number of pixels
within the same area is also greatly increased with the increment
of the resolution ratio, which requires that the area of single
pixel is further reduced. The OLED is a current-driven device, an
approximately linear corresponding relationship exists between the
light emitting brightness of the OLED and a current density, and
therefore, a driving current is required to be accordingly reduced
to reach the same current density after the area of the pixel is
reduced, in this way, there is a higher requirement for the
precision control of a driving circuit of the OLED. Meanwhile, in
order to reduce influences of change of a threshold voltage Vth
caused by a production process on an output current of the driving
circuit, the driving circuit is also required to have a Vth
compensation function.
SUMMARY
Embodiments of the present disclosure provide a pixel circuit, a
method for driving the same, a display panel and a display device.
The pixel circuit includes a first switching transistor, a second
switching transistor, a first capacitor, a second capacitor, a
driving transistor and a light emitting device;
wherein a gate electrode of the first switching transistor is
connected with a scanning signal end, a first electrode of the
first switching transistor is connected with a reference signal
end, and a second electrode of the first switching transistor is
connected with a gate electrode of the driving transistor;
a gate electrode of the second switching transistor is connected
with a light emitting control signal end, a first electrode of the
second switching transistor is connected with a first power supply
end, and a second electrode of the second switching transistor is
connected with a first electrode of the driving transistor;
a first end of the first capacitor is connected with a data signal
end, and a second end of the first capacitor is connected with a
second electrode of the driving transistor;
a first end of the second capacitor is connected with the gate
electrode of the driving transistor, and a second end of the second
capacitor is connected with the second electrode of the driving
transistor; and
an anode of the light emitting device is connected with the second
electrode of the driving transistor, and a cathode of the light
emitting device is connected with a second power supply end.
In some embodiments, in the above-mentioned pixel circuit according
to the embodiment of the present disclosure, a capacitance value of
the second capacitor is greater than that of the first
capacitor.
In some embodiments, in the above-mentioned pixel circuit according
to the embodiment of the present disclosure, each of the first
switching transistor, the second switching transistor and the
driving transistor is an N-type transistor.
Accordingly, an embodiment of the present disclosure further
provides a display panel including any one of the above-mentioned
pixel circuit according to the embodiment of the present
disclosure.
Accordingly, an embodiment of the present disclosure further
provides a display device including the above-mentioned display
panel according to the embodiment of the present disclosure.
Accordingly, an embodiment of the present disclosure further
provides a method for driving any one of the above-mentioned pixel
circuit according to the embodiment of the present disclosure,
including:
in a compensation phase: turning on the first switching transistor
by the scanning signal end, and loading a low-potential signal to
the gate electrode of the driving transistor by the reference
signal end; and turning on the second switching transistor by the
light emitting control signal end, and loading a high-potential
signal to the first electrode of the driving transistor by the
first power supply end;
in a data writing phase: turning on the first switching transistor
by the scanning signal end, and loading a high-potential signal to
the gate electrode of the driving transistor by the reference
signal end; turning off the second switching transistor by the
light emitting control signal end; and loading a data signal to the
second electrode of the driving transistor by the data signal end;
and
in a light emitting phase: turning off the first switching
transistor by the scanning signal end; and turning on the second
switching transistor by the light emitting control signal end, and
loading the high-potential signal to the first electrode of the
driving transistor by the first power supply end, for controlling
the driving transistor to drive the light emitting device to emit
light.
In some embodiments, in the above-mentioned method according to the
embodiment of the present disclosure, in the data writing phase,
time of turning off the first switching transistor by the scanning
signal end is earlier than that of stopping loading the data signal
by the data signal end.
In some embodiments, in the above-mentioned method according to the
embodiment of the present disclosure, in the data writing phase,
time of stopping loading the high-potential signal by the reference
signal end is later than that of turning off the first switching
transistor by the scanning signal end.
In some embodiments, in the above-mentioned method according to the
embodiment of the present disclosure, in the data writing phase,
time of stopping loading the high-potential signal by the reference
signal end is later than that of stopping loading the data signal
by the data signal end.
In some embodiments, in the above-mentioned method according to the
embodiment of the present disclosure, before the compensation
phase, the method further includes:
in an initialization phase: turning on the first switching
transistor by the scanning signal end, and loading the
low-potential signal to the gate electrode of the driving
transistor by the reference signal end; and turning on the second
switching transistor by the light emitting control signal end, and
loading the low-potential signal to the first electrode of the
driving transistor by the first power supply end.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a first schematic structural diagram of a pixel circuit
according to an embodiment of the present disclosure.
FIG. 2 is a first schematic flow diagram of a method for driving
the pixel circuit, according to an embodiment of the present
disclosure.
FIG. 3 is a second schematic flow diagram of the method for driving
the pixel circuit, according to the embodiment of the present
disclosure.
FIG. 4 is a schematic diagram of a circuit time sequence of the
pixel circuit as shown in FIG. 1.
FIG. 5 is a schematic structural diagram of the pixel circuit as
shown in FIG. 1 in an initialization phase.
FIG. 6 is a schematic structural diagram of the pixel circuit as
shown in FIG. 1 in a compensation phase.
FIG. 7 is a schematic structural diagram of the pixel circuit as
shown in FIG. 1 in a data writing phase.
FIG. 8 is a schematic structural diagram of the pixel circuit as
shown in FIG. 1 in a light emitting phase.
FIG. 9 is a simulation diagram of the pixel circuit according to
the embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In order to make objectives, technical solutions and advantages of
the present disclosure clearer, detailed descriptions of a pixel
circuit, a method for driving the same, a display panel and a
display device according to embodiments of the present disclosure
are explained in detail below in combination with the accompanying
drawings.
With the increment of the resolution ratio of the display, the area
of single pixel circuit is also reduced, and therefore, the
structure of the driving circuit is required to be simple as much
as possible during the design of the driving circuit to lower the
difficulty during Layout design. The driving circuit of the OLED is
divided into an negative channel metal oxide semiconductor (NMOS)
and a positive channel metal oxide semiconductor (PMOS) according
to used different thin film transistor (TFT) types, a source
electrode of the NMOS is generally located at an anode end during
an actual application, and therefore, an accompanying source
structure is generally adopted to guarantee the current stability
after a TFT is started. However, due to the adoption of the
structure, the threshold voltage Vth may not be completely
compensated under the influence of a capacitive coupling effect in
a compensation phase, and thus, the display effect of a panel may
be affected to a certain extent. Meanwhile, since the sub-threshold
of the NMOS is relatively small, a data voltage signal of the pixel
circuit is required to have higher precision to realize more
precise current control, in this way, there is a higher requirement
for the driving capability of an integrated circuit (IC), and
therefore, designing the pixel circuit to achieve higher precision
of the data voltage signal has certain application value.
An embodiment of the present disclosure provides a pixel circuit,
as shown in FIG. 1, including a first switching transistor T1, a
second switching transistor T2, a first capacitor C1, a second
capacitor C2, a driving transistor DT and a light emitting device
L.
Agate electrode of the first switching transistor T1 is connected
with a scanning signal end Gate, a first electrode of the first
switching transistor T1 is connected with a reference signal end
Ref, and a second electrode of the first switching transistor T1 is
connected with a gate electrode of the driving transistor DT; in
some embodiments, when the first switching transistor T1 is in a
turned-on state under control of the scanning signal end Gate, a
reference signal of the reference signal end Ref is provided for
the gate electrode (N1 point) of the driving transistor DT.
A gate electrode of the second switching transistor T2 is connected
with a light emitting control signal end EM, a first electrode of
the second switching transistor T2 is connected with a first power
supply end VDD, and a second electrode of the second switching
transistor T2 is connected with a first electrode of the driving
transistor DT; in some embodiments, when the second switching
transistor T2 is in a turned-on state under control of the light
emitting control signal end EM, a voltage of the first power supply
end VDD is provided for the first electrode of the driving
transistor DT, and a driving current output by a second electrode
of the driving transistor DT is output to the light emitting device
L to drive the light emitting device L to emit light.
A first end of the first capacitor C1 is connected with a data
signal end Data, and a second end of the first capacitor C1 is
connected with the second electrode of the driving transistor DT;
in some embodiments, the data signal end Data inputs a data signal
to the second electrode of the driving transistor DT through the
first capacitor C1.
A first end of the second capacitor C2 is connected with the gate
electrode of the driving transistor DT, and a second end of the
second capacitor C2 is connected with the second electrode of the
driving transistor DT; in some embodiments, the second capacitor C2
is charged under joint control of a gate electrode (N1 point)
signal of the driving transistor DT and a second electrode signal
of the driving transistor DT, and the second capacitor C2 is
discharged under joint control of the gate electrode (N1 point)
signal of the driving transistor DT and the second electrode signal
of the driving transistor DT; when the light emitting device L is
in a light emitting state, a voltage difference of the gate
electrode (N1 point) of the driving transistor DT and the second
electrode of the driving transistor DT is kept stable, so as to
ensure that the driving transistor DT outputs a stable current.
An anode of the light emitting device L is connected with the
second electrode of the driving transistor DT, and a cathode of the
light emitting device L is connected with a second power supply end
VSS.
According to the above-mentioned pixel circuit according to the
embodiment of the present disclosure, by coordination of the
above-mentioned three transistors and two capacitors, an input
range of a data voltage of the data signal end may be extended, the
extended range is related to capacitance values of the two
capacitors, and therefore, the pixel circuit according to the
present disclosure may extend the input range of the data voltage
on the basis that driving capability of a driving IC is not
improved, namely the data voltage may have a wider input range on
the basis that a cost is not increased, so that higher-precision
current control is realized, and precision of a display frame is
improved. In addition, by coordination of the above-mentioned three
transistors and two capacitors, the current output by the driving
transistor in the pixel circuit may also be only related to the
data voltage of the data signal end and a reference voltage of the
reference signal end, but is unrelated to a threshold voltage of
the driving transistor, in this way, influences of the threshold
voltage of the driving transistor on the current output by the
driving transistor may be avoided, so that the current output by
the driving transistor may be kept stable, and furthermore,
brightness uniformity of a frame in a display area in a display
device may be improved.
In some embodiments, in the above-mentioned pixel circuit according
to the embodiment of the present disclosure, the second capacitor
has to keep the voltage difference of the gate electrode of the
driving transistor and the second electrode of the driving
transistor stable for a long time to ensure that the current
flowing towards the light emitting device is constant, and
therefore, the capacitance value of the second capacitor is
relatively large. In order to reduce an area occupied by a space
and guarantee design feasibility of the pixel circuit, the
capacitance value of the first capacitor is relatively small.
Therefore, in some embodiments, in the above-mentioned pixel
circuit according to the embodiment of the present disclosure, the
capacitance value of the second capacitor is greater than that of
the first capacitor.
Further, in some embodiments, in the above-mentioned pixel circuit
according to the embodiment of the present disclosure, as shown in
FIG. 1, each of the first switching transistor T1, the second
switching transistor T2 and the driving transistor DT is an N-type
transistor.
In some embodiments, in the above-mentioned pixel circuit according
to the embodiment of the present disclosure, the N-type transistors
are turned on under an action of a high potential and are turned
off under an action of a low potential.
In some embodiments, in the above-mentioned pixel circuit according
to the embodiment of the present disclosure, the light emitting
device is generally an OLED, and the light emitting device emits
light under an action of a current of the driving transistor in a
saturated state. In addition, generally, the light emitting device
has a threshold voltage, and the light emitting device emits light
when voltages at two ends of the light emitting device are greater
than or equal to the threshold voltage.
In some embodiments, in the above-mentioned pixel circuit according
to the embodiment of the present disclosure, the voltage of the
first power supply end VDD is generally a high-level voltage, and a
voltage of the second power supply end VSS is generally grounded or
is a low-level voltage.
It should be explained that, in the above-mentioned pixel circuit
according to the embodiment of the present disclosure, each of the
driving transistor and the switching transistors may be a TFT or a
metal oxide semiconductor (MOS), limitations thereof are omitted
herein.
In some embodiments, functions of the first electrodes and second
electrodes of these switching transistors may be exchanged
according to different types of the switching transistors and
different signals of the signal ends, wherein the first electrodes
may be source electrodes, the second electrodes may be drain
electrodes, or the first electrodes may be the drain electrodes,
the second electrodes may be the source electrodes, specific
differentiations thereof are omitted herein.
Based on the same inventive concept, an embodiment of the present
disclosure further provides a method for driving any one of the
above-mentioned pixel circuit according to the embodiment of the
present disclosure, as shown in FIG. 2, and the method
includes.
S201, in a compensation phase: turning on the first switching
transistor by the scanning signal end, and loading a low-potential
signal to the gate electrode of the driving transistor by the
reference signal end; and turning on the second switching
transistor by the light emitting control signal end, and loading a
high-potential signal to the first electrode of the driving
transistor by the first power supply end.
S202, in a data writing phase: turning on the first switching
transistor by the scanning signal end, and loading a high-potential
signal to the gate electrode of the driving transistor by the
reference signal end; turning off the second switching transistor
by the light emitting control signal end; and loading a data signal
to the second electrode of the driving transistor by the data
signal end.
S203, in a light emitting phase: turning off the first switching
transistor by the scanning signal end; and turning on the second
switching transistor by the light emitting control signal end, and
loading the high-potential signal to the first electrode of the
driving transistor by the first power supply end, for controlling
the driving transistor to drive the light emitting device to emit
light.
According to the method for driving the above-mentioned pixel
circuit according to the embodiment of the present disclosure, an
input range of a data voltage of the data signal end may be
extended, the extended range is related to capacitance values of
the two capacitors, and therefore, the pixel circuit according to
the present disclosure may extend the input range of the data
voltage on the basis that driving capability of a driving IC is not
improved, namely the data voltage may have a wider input range on
the basis that a cost is not increased, so that higher-precision
current control is realized, and precision of a display frame is
improved. In addition, a current output by the driving transistor
in the pixel circuit may also be only related to the data voltage
of the data signal end and a reference voltage of the reference
signal end, but is unrelated to a threshold voltage of the driving
transistor, in this way, influences of the threshold voltage of the
driving transistor on the current output by the driving transistor
may be avoided, so that the current output by the driving
transistor may be kept stable, and furthermore, brightness
uniformity of a frame in a display area in a display device may be
improved.
Further, in some embodiments, in order to prevent a signal of a
last frame from affecting a signal of a next frame, in the
above-mentioned method according to the embodiment of the present
disclosure, as shown in FIG. 3, before the compensation phase of
each frame, the method further includes.
S201', in an initialization phase: turning on the first switching
transistor by the scanning signal end, and loading the
low-potential signal to the gate electrode of the driving
transistor by the reference signal end; and turning on the second
switching transistor by the light emitting control signal end, and
loading the low-potential signal to the first electrode of the
driving transistor by the first power supply end.
Further, in some embodiments, in the above-mentioned method
according to the embodiment of the present disclosure, as shown in
FIG. 4, in the data writing phase T3: the time of turning off the
first switching transistor T1 by the scanning signal end Gate is
earlier than that of stopping loading the data signal by the data
signal end Data. Thus, it may be ensured that the data signal of
the data signal end Data may be loaded to the second electrode of
the driving transistor DT.
Further, in some embodiments, in the above-mentioned method
according to the embodiment of the present disclosure, as shown in
FIG. 4, in the data writing phase T3: the time of stopping loading
the high-potential signal by the reference signal end Ref is later
than that of turning off the first switching transistor T1 by the
scanning signal end Gate.
Further, in some embodiments, in the above-mentioned method
according to the embodiment of the present disclosure, as shown in
FIG. 4, in the data writing phase T3: the time of stopping loading
the high-potential signal by the reference signal end Ref is later
than that of stopping loading the data signal by the data signal
end Data.
Of course, in some embodiments, in the above-mentioned method
according to the embodiment of the present disclosure, the time of
stopping loading the high-potential signal by the reference signal
end Ref may also be same as that of turning off the first switching
transistor T1 by the scanning signal end Gate.
A working process of the above-mentioned pixel circuit according to
the embodiment of the present disclosure is described below with
the pixel circuit as shown in FIG. 1 as an example in combination
with a circuit time sequence diagram. In the following description,
1 represents for a high potential, and 0 represents for a low
potential. It should be noted that 1 and 0 are logic potentials and
are merely intended to better explain the specific working process
of the embodiment of the present disclosure, rather than a
potential applied to the gate electrode of each of the switching
transistors during specific implementation.
As shown in FIG. 1, the driving transistor DT is an N-type
transistor, and both the switching transistors are N-type
transistors; and corresponding input time sequence diagrams are
shown in FIG. 4. Specifically, four phases including an
initialization phase T1, a compensation phase T2, a data writing
phase T3 and a light emitting phase T4 in the input time sequence
diagram as shown in FIG. 4 are selected.
In the initialization phase T1, EM=1, Gate=1, Data=0, Ref=0 and
VDD=0.
As shown in FIG. 5, illustrating a schematic diagram of a working
condition of the initialization phase of the pixel circuit of the
present disclosure, all the first switching transistor T1, the
second switching transistor T2 and the driving transistor DT are in
a turned-on state. The low-potential signal of the reference signal
end Ref is provided for the gate electrode (N1 point) of the
driving transistor DT by the turned-on first switching transistor
T1, to initialize a potential of the gate electrode (N1 point) of
the driving transistor DT; and a potential of the anode of the
light emitting device L is decreased by the low-potential signal of
the first power supply end VDD, so as to initialize the potential
of the anode of the light emitting device L. In the phase, it is
assumed that the potential of the N1 point is V1 (Ref is a
low-potential signal and is set as 0 V), and a potential of an N2
point is the low-potential signal of the first power supply end
VDD.
In the compensation phase T2, EM=1, Gate=1, Data=0, Ref=0 and
VDD=1.
As shown in FIG. 6, illustrating a schematic diagram of a working
condition of the compensation phase of the pixel circuit of the
present disclosure, all the first switching transistor T1, the
second switching transistor T2 and the driving transistor DT are in
a turned-on state. The low-potential signal of the reference signal
end Ref is still provided for the N1 point by the turned-on first
switching transistor T1, and the potential of the N1 point is still
V1 (0 V); since VDD=1, a threshold voltage Vth of the driving
transistor DT is compensated to the second electrode (N2 point) of
the driving transistor DT in the phase, and the potential of the N2
point is V1-Vth.
In the data writing phase T3, EM=0, Gate=1 to 0, Data=1 to 0, Ref=1
and VDD=1.
As shown in FIG. 7, illustrating a schematic diagram of a working
condition of the data writing phase of the pixel circuit of the
present disclosure, the second switching transistor T2 is in a
turned-off state, firstly, a signal of the scanning signal end Gate
is at a high potential to turn on the first switching transistor
T1, the high-potential signal of the reference signal end Ref is
provided for the N1 point, and a signal of the data signal end Data
is at a high potential to complete writing of the data signal;
then, the signal of the scanning signal end Gate is at a low
potential to turn off the first switching transistor T1, and after
the first switching transistor T1 is turned off, both the signal of
the data signal end Data and the signal of the reference signal end
Ref become low-potential signals. In the phase, before the signal
of the data signal end Data is decreased, the potential of the N1
point is V2 (the high-potential signal of the end Ref), and due to
a serial voltage division effect of the first capacitor C1 and the
second capacitor C2, the potential of the N2 point is
.times..times..times..times..times..times..times..times..times.
##EQU00001## since V1=0, a potential difference of the N1 point and
the N2 point is
.times..times..times..times..times. ##EQU00002## Since both the N1
point and the N2 point are in a suspension joint state after the
first switching transistor T1 is turned off, decrease of the signal
of the data signal end Data is incapable of affecting the potential
difference of the N1 point and the N2 point.
It is assumed that the threshold voltage of the driving transistor
DT is Vth=0, the potential difference of the N1 point and the N2
point is (V2-VData), and the range of a value of a current flowing
into the light emitting device L is 1 uA-5 uA, the above-mentioned
range of the current value is met when the data signal input to the
data signal end Data by the driving IC is 0-3 V in the related art.
The driving capability of the driving IC is limited, so that only
four data voltages 0 V, 1 V, 2 V and 3 V may be input to the data
signal end Data in the related art, input of the four data voltages
may ensure that the obtained potential difference of the N1 point
and the N2 point is within a preset range, it is ensured that the
current flowing into the light emitting device L is effective. The
obtained current value is relatively small due to the relatively
small range of the data voltages, an OLED display panel is driven
by a current, and the current flowing into the light emitting
device L may not be controlled at higher precision, so that the
display frame is not delicate enough. For the above-mentioned pixel
circuit according to the embodiment of the present disclosure, when
Vth=0, the potential difference of the N1 point and the N2 point
is
.times..times..times..times..times. ##EQU00003## it may be seen
that
.times..times..times.< ##EQU00004## If a range of the potential
difference of the N1 point and the N2 point, which is same as that
in the related art, is expected to be obtained, the data voltage
VData of the data signal end Data in the present disclosure may be
extended by
.times..times..times. ##EQU00005## times; it is assumed that
.times..times..times. ##EQU00006## the data voltage VData of the
data signal end Data may be doubled, namely the driving IC may
input seven data voltages 0 V, 1 V, 2 V, 3 V, 4 V, 5 V and 6 V to
the data signal end Data, different current values corresponding to
the seven data voltages are all effective current values.
Therefore, due to coordination of the first capacitor C1 and the
second capacitor C2 in the pixel circuit of the present disclosure,
the input range of the data voltage of the data signal end may be
extended, more effective currents are achieved, so that the display
frame is more delicate; and the extended range is related to the
capacitance values of the two capacitors, and therefore, the pixel
circuit according to the present disclosure may extend the input
range of the data voltage on the basis that the driving capability
of the driving IC is not improved, namely the data voltage may have
higher precision on the basis that the cost is not increased, so
that more precise current control is realized, and the precision of
the display frame is improved.
It should be noted that the above-mentioned ranges of the potential
difference of the N1 point and the N2 point, ranges of the data
voltage and ranges of the current value are merely illustrated, in
order to explain that the pixel circuit according to the present
disclosure may extend the input range of the data voltage on the
basis that the driving capability of the driving IC is not
improved, in some embodiments, the ranges of the potential
difference of the N1 point and the N2 point, ranges of the data
voltage and ranges of the current value may be determined according
to an actual demand.
In the light emitting phase T4, EM=1, Gate=0, Data=0, Ref=0 and
VDD=1.
As shown in FIG. 8, illustrating a schematic diagram of a working
condition of the light emitting phase of the pixel circuit of the
present disclosure; the first switching transistor T1 is in a
turned-off state, both the second switching transistor T2 and the
driving transistor DT are in a turned-on state, the voltage of the
first electrode of the driving transistor DT is the voltage of the
first power supply end VDD, the driving transistor DT works in a
saturated state, and known from a current characteristic in the
saturated state, a working current I.sub.OLED flowing through the
driving transistor DT and being used for driving the light emitting
device L to emit light meets a formula:
.times..function..times..times..times..times..times..times..times..functi-
on..times..times..times..times..times..times..times..function..times..time-
s..times..times..times..times. ##EQU00007##
Wherein K is a structural parameter, is relatively stable in the
same structure and may be regarded as a constant. Therefore, it may
be seen that the working current I.sub.OLED of the light emitting
device L has not been affected by the threshold voltage Vth of the
driving transistor DT and is only related to the data voltage VData
of the data signal end Data and the reference voltage V2 of the
reference signal end Ref, so that influences of drifting of the
threshold voltage Vth of the driving transistor DT on the working
current I.sub.OLED of the light emitting device L due to technical
processes and long-term operation are thoroughly solved, and
furthermore, the display non-uniformity of the panel is improved.
Moreover, the above-mentioned pixel circuit according to the
embodiment of the present disclosure may realize compensation of
the threshold voltage Vth of the driving transistor DT by only
adopting the three transistors and the two capacitors, so as to be
relatively simple in structure.
Moreover, in the present disclosure, time sequences of the pixel
circuit according to the above-mentioned embodiment in the four
phases are further simulated, as shown in FIG. 9. Seen from a
simulation result of FIG. 9, the time sequences are basically
consistent with the time sequence diagram as shown in FIG. 4, and
potentials of the N1 point and the N2 point are also basically
consistent, so that it may be verified that the working current
I.sub.OLED of the light emitting device L is really not affected by
the threshold voltage Vth of the driving transistor DT in the pixel
circuit according to the embodiment of the present disclosure.
Based on the same inventive concept, an embodiment of the present
disclosure further provides a display panel including any one of
the above-mentioned pixel circuit according to the embodiment of
the present disclosure. A principle of solving problems of the
display panel is similar to that of the above-mentioned pixel
circuit, and therefore, implementation of the display panel may
refer to that of the above-mentioned pixel circuit, repetitions
thereof are omitted herein.
In some embodiments, in the above-mentioned display panel according
to the embodiment of the present disclosure, the display panel may
be an OLED display panel.
Based on the same inventive concept, an embodiment of the present
disclosure further provides a display device including the
above-mentioned display panel according to the embodiment of the
present disclosure. The display device may be any one product or
component with a display function, such as a mobile phone, a tablet
personal computer, a television, a display, a notebook computer, a
digital photo frame and a navigator. Those ordinary skilled in the
art should understand that other essential components of the
display device are provided, descriptions thereof are omitted
herein, and they should not be regarded as limitations on the
present disclosure. Implementation of the display device may refer
to the embodiment of the above-mentioned pixel circuit, repetitions
thereof are omitted herein.
According to the pixel circuit, the method for driving the same,
the display panel and the display device according to the
embodiments of the present disclosure, the pixel circuit includes
the first switching transistor, the second switching transistor,
the first capacitor, the second capacitor, the driving transistor
and the light emitting device, wherein the gate electrode of the
first switching transistor is connected with the scanning signal
end, the first electrode of the first switching transistor is
connected with the reference signal end, and the second electrode
of the first switching transistor is connected with the gate
electrode of the driving transistor; the gate electrode of the
second switching transistor is connected with the light emitting
control signal end, the first electrode of the second switching
transistor is connected with the first power supply end, and the
second electrode of the second switching transistor is connected
with the first electrode of the driving transistor; the first end
of the first capacitor is connected with the data signal end, and
the second end of the first capacitor is connected with the second
electrode of the driving transistor; the first end of the second
capacitor is connected with the gate electrode of the driving
transistor, and the second end of the second capacitor is connected
with the second electrode of the driving transistor; and the anode
of the light emitting device is connected with the second electrode
of the driving transistor, and the cathode of the light emitting
device is connected with the second power supply end. Therefore, by
coordination of the above-mentioned three transistors and two
capacitors, the input range of the data voltage of the data signal
end may be extended, the extended range is related to the
capacitance values of the two capacitors, and therefore, the pixel
circuit according to the present disclosure may extend the input
range of the data voltage on the basis that the driving capability
of the driving IC is not improved, namely the data voltage may have
a wider input range on the basis that the cost is not increased, so
that higher-precision current control is realized, and the
precision of the display frame is improved. In addition, by
coordination of the above-mentioned three transistors and two
capacitors, the current output by the driving transistor in the
pixel circuit may also be only related to the data voltage of the
data signal end and the reference voltage of the reference signal
end, but is unrelated to the threshold voltage of the driving
transistor, in this way, influences of the threshold voltage of the
driving transistor on the current output by the driving transistor
may be avoided, so that the current output by the driving
transistor may be kept stable, and furthermore, the brightness
uniformity of the frame in the display area in the display device
may be improved.
Obviously, those skilled in the art can make various alterations
and transformations on the present disclosure without departing
from the spirits and scopes of the present disclosure. In this way,
if these alterations and transformations of the present disclosure
fall within the scope of the claims of the present disclosure and
equivalent technologies of the claims, the present disclosure is
also intended to include these alterations and transformations.
* * * * *